.nav {
    position: fixed;
    top: 0;
    left: 0;
    display: flex;
    width: 100%;
    height: 44px;
    line-height: 44px;
    font-size: 18px;
    z-index: 99;
    background-color: hsla(0, 0%, 4%, .2);
}

.back {
    position: absolute;
    left: 15px;
    font-size: 25px;
    color: #fff;
}

.center {
    margin: 0 auto;
    width: 70%;
    height: 44px;
    font-size: 18px;
    font-weight: 700;
    color: #fff;
    text-align: center;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}